Available, state of the art, secure communication systems normally are based on electronic encryption to achieve security. These secure communication systems take data and, using special algorithms, process it in a computer into a form that cannot be reconverted into usable data unless the receiver of the encrypted data has the proper algorithms, conversion electronics and software key codes. The encryption and decryption processes are complex and computer processor intensive, requiring processor speeds approximately an order of magnitude faster than the effective data transmission rate of the communication system over which the data is to be sent. When data is to be transmitted, computer to computer, the relative slowness of the encryption process either slows down the transmission rate or requires the users to use expensive distributed processing and multiplex schemes.
Electronic encryption methods are practical for point to point secure communications, but are difficult to implement into communication networks because of the difficulty of handling codes and code changes for each user on the network. Also, the handling of multiple codes at various locations increases the chance that an unauthorized entity will be able to gain access to the codes and be able to decrypt data. In most instances the communication lines over which the secure data is transmitted, are available for unscrupulous persons to tap into the data. In most instances the communication lines over which the secure data is transmitted, are available for unscrupulous persons to tap into the data. If the code has been obtained and access is possible, such persons can intercept data and/or change data without being detected.
Therefore, what is needed are secure communication systems which can transfer data at extremely high speeds over a network and which do not require complex codes, code changes or prevention of access to communication lines.
There are advanced high speed systems, which do not need encryption because the data transferred thereover is in a physical form that defies interception and demodulation, which are based on Sagnac interferometers. Such Sagnac interferometer based secure fiber optic communication systems are described in U.S. patent application Ser. Nos. 880,664 and 880,685, filed Jun. 11, 1986 by Eric Udd and are assigned to McDonnel Douglas Corporation now respectively U.S. Pat. Nos. 5,223,967 and 5,274,488. Point to point systems are described in those applications which are at least as secure as any other secure communication system, which can operate at extremely high data rates, the rate usually being limited by the input and output electronics rather than by limitations of the system itself, and which cannot be tapped at any location along the system to gain unauthorized access to the data thereon.